The invention concerns systems for optically imaging objects, in particular information-carrying optical patterns of codes, on a detection device and in particular on a CCD or CMOS element with the aid of a pinhole aperture. The invention especially concerns systems that have devices which substantially compensate the imaging defects caused by the pinhole aperture and in particular the system-inherent peripheral decrease in brightness of an image of the object formed by a pinhole aperture on the detection device.
In addition the invention concerns systems for capturing optical information which comprise such a system for optically imaging an object that carries optical information and an in-line evaluation device which collects the optical information of the object from the image of the object, formed on the detector device and provides this information for further processing or display.
In addition, the invention concerns test element analytical systems comprising at least one test element and an evaluation device which contain such systems according to the invention for collecting optical information.
Finally, the invention concerns methods for optically imaging objects on a detection device by a pinhole aperture which can substantially compensate the imaging defects caused by the pinhole aperture and in particular the system-inherent peripheral decrease in brightness of an image of the object formed by a pinhole aperture on the detection device.
The optical imaging of objects on detection devices plays a major role in many technical fields. Thus the optical imaging of one-dimensional or two-dimensional optical patterns on detection devices that are usually in special reading systems such as code readers or scanners, is used to collect information, on the objects which carry these optical patterns and to transfer the information to an in-line evaluation system.
Optical patterns which are often used to store or transfer information are for example one-dimensional (1D, for example barcodes) or two-dimensional (2D, for example data matrix codes) codes which are applied to objects, for example printed onto or glued onto objects and contain, information on this object. In this case the information is coded in the optical pattern of the code. An image thereof is formed on a detection device which firstly records the image of the pattern. Subsequently the information of the imaged object can be collected therefrom and provided for further pressing or display. Thus, for example, structural units, individual components, intermediate and also final products can be unequivocally identified and controlled with such a code which, among others, enables a control of production and storage and a traceability of products if errors should occur. Typical fields of application of such codes are storage and materials-handling technology, quality assurance, material monitoring, production control, sample identification in pharmaceutics and the health system, in the automobile industry, in chemical and biomedical analyzers and for document handling.
Such optical systems are also used to record optical patterns especially in chemical and diagnostic analytical systems and especially in test element analytical systems. In such test element analytical systems optical codes which are on the respective test element or on an object that is specialty provided for this purpose such as a batch-specific coding object, are used primarily to deliver specific information to the evaluation device on the test that is being used in each case and/or the special test element. Such test element analytical systems are described for example in the German Patent Application with the file number 102004011648.2.
The optical reading systems, used in industrial applications usually employ lens optics in reflection optical methods which form an image of the optical pattern on a detection device. Other designs are for example realized in scanners which use partially transparent optical patterns or codes in a transmission process. Whereas, one-dimensional codes can usually be recorded relatively simply by employing line sensors or scanners that move relatively to the code-carrying object, two-dimensional optical patterns such as 2D codes are firstly imaged on a detection, device and these images are subsequently evaluated, usually by special software algorithms. Such reading systems for two-dimensional-optical patterns usually employ optical matrix sensors such as CCD or CMOS sensors, as detection devices.
For a good imaging quality of the imaging system it is important that these systems have imaging properties that result in a substantially uniform system-inherent brightness distribution in the detection plane. In this connection the term system-inherent brightness distribution in the detection plane is understood to mean that it refers to the brightness distribution of the image of a uniform object and in particular a homogeneous and especially uniformally structured and uniformly colored surface on a detection device which is located in the detection plane. Such a brightness distribution allows information to be obtained on the fundamental imaging properties of the optical system. An image of such a uniform object can be regarded as a type of background image which represents the system-inherent imaging properties including its system-inherent imaging defects. An object that is to be imaged which carries information must be distinguishable from such a system-inherent background image for example in the form of defined areas of a different brightness or color. If a system-inherent background image already results in appreciable differences in brightness in the detection plane, these system-inherent differences in brightness would be superimposed on the differences in brightness that are due to the actual information-carrying object that is to be imaged and are desired and necessary for information transfer, for example in the form of areas that are too light or dark. This would considerably complicate, falsify or prevent the acquisition and evaluation of the true information to be transferred.
Various solutions have been proposed in the prior art to achieve the most homogeneous system-inherent brightness distribution, in the detection plane:
Thus, for examples the 2D code reader “Quadras” from the Microsan Company (Freising, Germany) has 20 individual high-performance LEDs as light sources to illuminate the object as homogeneously as possible.
The German laid-open document DE 4221069 describes an optical device for imaging optical patterns such as a barcode that are imaged on a photosensor. The optical device comprises an imaging lens to image the barcode and a CCD line sensor to record and evaluate the information of the image of the barcode. The system also has an attenuation device that is arranged between the barcode and the line sensor and is designed such that the system-inherent brightness distribution on the sensor becomes more uniform despite the construction-related influence by the imaging lens. In this connection DE 4221069 reaches attenuation elements which comprise an optical element which is able to attenuate the intensity of certain spatial areas of a light beam that impinges on the line sensor after being emitted from the object to be imaged. In this connection DE 4221069 teaches in particular mirror elements that are provided with a coating which, has a lower refractive index in the central area than in the periphery and are thus suitable as attenuation dements according to the invention. Furthermore, DE 4221069 teaches ND (neutral density) filters as attenuation elements with a lower transmission factor in the central area than in the periphery which can be used as light attenuating filters in the optical path between the code to be imaged and the detection device.
Other factors have to be taken into consideration for an application of imaging systems especially in mobile instruments or hand-held systems such as hand scanners or portable test element analytical systems:                Since such systems are often manufactured in large numbers it is advantageous to integrate imaging systems that are as simple and cheap as possible into these systems or instruments. They must nevertheless fulfil certain requirements with regard to the imaging quality in order to ensure the optical information which is contained in the objects to be imaged is accurately recorded and evaluated.        Many of the conventional systems which employ a scanning movement relative to the object to be imaged have a relatively large constructed space which, among others, is due to their lens systems and the devices that control the movement of the object relative to the detection device. Since especially test element analytical systems are often designed as portable hand-held instruments, it is desirable that such systems have the smallest possible constructional size that should be in the range of a few cubic centimeters.        Simple and cheap imaging systems usually employ a transmission method which means that the object to be imaged is irradiated by a light source and imaged on a detection device which is located on the side opposite to the light source. It is inherent to the system that such systems require a large constructional space since the light source, object to be imaged and detection device have to be arranged one behind the other and they are therefore only of limited suitability for use in portable systems. Moreover, the object to he imaged must have certain optical properties in order for such transmission methods to be used at all. Thus, for example, optical codes must have at least partially transparent areas in order that their information can be read by such systems. Consequently, such imaging systems are unsuitable for many fields of application.        
No systems are known from the prior art for optically imaging objects which are characterized by a combination of a very simple and cheap design, the smallest possible structural space, the ability to form an image of the object to be imaged on the detection device without a movement of the imaging system relative to the object and very reliable reading. In particular, the known imaging systems are only of limited suitability for incorporation into small and portable systems and in particular into diagnostic test element analytical systems. In particular, no simple imaging systems are known which achieve a very uniform system-inherent brightness distribution in the detection plane using simple and cost-efficient means.